Remove KZG verification from local block production and blobs fetched from the EL (#7713)

#7700


  As described in title, the EL already performs KZG verification on all blobs when they entered the mempool, so it's redundant to perform extra validation on blobs returned from the EL.

This PR removes
- KZG verification for both blobs and data columns during block production
- KZG verification for data columns after fetch engine blobs call. I have not done this for blobs because it requires extra changes to check the observed cache, and doesn't feel like it's a worthy optimisation given the number of blobs per block.

This PR does not remove KZG verification on the block publishing path yet.

beacon_node/beacon_chain/src/data_column_verification.rs

@@ -266,6 +266,12 @@ impl<E: EthSpec> KzgVerifiedDataColumn<E> {
         verify_kzg_for_data_column(data_column, kzg)
     }
 
+    /// Mark a data column as KZG verified. Caller must ONLY use this on columns constructed
+    /// from EL blobs.
+    pub fn from_execution_verified(data_column: Arc<DataColumnSidecar<E>>) -> Self {
+        Self { data: data_column }
+    }
+
     /// Create a `KzgVerifiedDataColumn` from `DataColumnSidecar` for testing ONLY.
     pub(crate) fn __new_for_testing(data_column: Arc<DataColumnSidecar<E>>) -> Self {
         Self { data: data_column }